Incandescent filament lamp



D. E. STRATY ET AL. INCANDES'CENT FILAMENT LAMP Filed April 2 ,1954

July 9, 1935.

Patented 9, '1935 PAT ENT-

OFFICE ,n vcannnscnn'r mnmm'r LAMP-i Doris n. amt, and Stephen Straty, Milwaukee. Wis.

f p Application April 28, 1024. Serial No. 722.992

c Claims. (01. ire-24) This invention relates to an improvement in incandescent filament lamps, and more particularly 'to an electric lamp for use in. series relation to other similar lamps, and provided with a shunting device which is thermally responsive to the filament of the lamp with which it is associated. I j

Lamps to be grouped in series are now, and have been for some time, in common use. Examples of such use are the lighting arrangement generally used for decorative purposes, and for trimming Christmas trees, where it is the usual practice to use filament lamps having no means for establishing a shunt path around the lamp when its filament becomes ruptured or burned out. Therefore, in the event the filament of any lamp in the circuit becomes broken or inoperative, the circuit is opened, with the result that the remainder of the lamps are extinguished. Many devices have been proposed for overcoming this inherent defect of series lamps, but such devices have met with little, it any, success in the art because of their impractical, expensive and generally complicated construction.

It is, therefore, an object of this invention to, so construct an incandescent filament lamp that in case the filament of the same is ruptured or for any reason'becomes inoperative, a new path for the electric current is automatically established so as to short-circuit or shunt the detective lamp from the system, leaving the remainder of the lamps in the circuit unafiected.

It is also an object or this invention to provide a lamp construction which will facilitate the detection of a burned-out or inoperative lamp in a series lighting circuit.

'A further object or this invention is to provide a simplified and practical shunting device for an incandescent filament lamp, which may be cheaply producedand without material alteration or modification of manufacturing processes or machine methods now employed in the quantity production of incandescent filament lamps.

Other objects and attendant advantages oi. this invention .will be manifest from the detailed description following.

In the attached drawing, which discloses a preferred embodiment of this invention: a

Figure 1 is an elevatlonal view 01' a lamp conv struction embodying this invention;

Figure 2 is a. detail view oi. the thermostatic device shown in Figure 1; and

Figure 3 is a detail view of a modified thermostatic device.

Eldon-in; to the drawing, the lamp of our invention comprises a sealed enclosure or glass bulb I, having an externally threaded base 2, and glass stem 3, allot conventional construction. Lead-in wires! are mounted in the glass stem 3 and at their upper ends support, in any suitable manner, an incandescent light-emitting filament 5.

Each lead 4, in addition, carries an armor ther- -mostatic element 6, whichmay be formed, for

example, of two metal strips l, 8 having different co-efiicients of expansion. The inner strip 1 may 10 be made of metal having a greater .co-efi'icient of expansion than the metal of outer strip 8. The lower ends 9 of the arms 6 are secured to leads 4 in any suitable manner, as by welding. Each arm 6 at its outer end l0 carries a contact member or button ll. These latter contacts are of suitably chosen material having 'a proper resistance value to insure the passage ofv suificient current through thefilament to substantially-heat the same when current is supplied thereto.

Referring now to the operation of the lamp, Figure 1 shows'the position assumed by the arms 6 when the filament is thermally inactive or cold. Wheh the lamp is placed in circuit, and current allowed to fiow through the circuit, current fiows through both filament 5 and shunt path 6, I I, I], 6. Filament 5 thus becomes heated and this heat is transmitted to the arms 6. The latter, by the unequal expansion of their component metal strips 1, 8, from which'each arm is formed, move oppositely at the outer ends ill to separate the contacts H (see Fig. 2). As long as filament 5 remains unbroken and incandenscent or thermally active, arms 6 will remain in a warped position 85 and maintain the contacts I I in the separated or open-circuit position shown in Fig. 2. In the event filament 5 becomes broken or burned out during the course of use, current ceases to fiow through same, and the filament becomes cold or 40 thermally inactive. Immediately the filament becomes cool or thermally inactive, the thermostatic arms 6 will begin to cool. This cooling of arms 6 causes their return to the position shown in Figure 1. Contacts H will then abut each other, and as a path for current flow through the lamp, by way of the shunt path formed by leads 4, arms 6, and contacts II will be established. This shunt path will serve to maintain the lamp circuit closed, and thereby insure a supply of current to the other lights in the circuit; As all of the lights but one are now lit, the lamp with the burned-out or broken filament is readily detected, and may be replaced;

When the filament of a lamp becomes inoperative during its use in a series circuit, only a short interval oi time may elapse before the arms 6 cool sufliciently to bring contacts I I together and close the shunt circuit. During such interval, the circuit will be open and all of the lamps will be extinguished. A signal, therefore, will be given that one of the lights is no longer of use.

A modified construction for the thermostatic device is shown in Figure 3, where only one Of the two arms mounted on lead-in wires 4 is constructed as a thermostatic element. This arm (I2) is similar in detail to the arms 6 shown in Figures 1 and 2, being formed, for example, of two metal strips I, 8 having different coefiicients of expansion. The other arm I3 is formed in any suitable way so as to serve as a stationary conducting support for the contact element II which it carries. Arm I2 which also carries a contact element I I operates in the same manner as the arms 6 of Figures 1 and 2. Thus, when filament 5 becomes heated, the heat is transmitted to the thermostatic element I2, and the latter moves away from the stationary arm I3 to effect separation of contact elements II. When filament 5 cools or-burns out, thermostatic element I2 will move toward the stationary arm I3 to close the gap between contact elements I I, and establish a path for current in shunt to the filament.

While only two embodiments of this invention have been shown and described, other forms and modifications embodying the invention may be readily devised within the spirit and scope of the invention, as defined in the following claims.

We claim:

1. An electric lamp for use in series lighting comprising, a sealed enclosure, a pair of filament supporting leads extending into said enclosure, a filament connecting the ends of said leads, and a thermostatic device for establishing a conducting path across said leads in shunt to said filament when the latter is thermally inactive, said device comprising, an arm mounted on each of said leads and electrically connected thereto, and a pair of electrical contacts supported in abutting position by the free ends of said arms, at least one of said arms being a bi-metallic member responsive to temperature changes in said filament and operative to bring said contacts together whenever said filament is thermally inactive, said contacts having such ohmic resistance that when in the closed position current will fiow through said filament sufiicient to heat the latter and cause said thermostatic device to assume the open circuit position.

2. An electric lamp for use in series lighting comprising, a sealed enclosure, a pair of'leads extending into said enclosure, a filament connecting the ends of said leads, and a thermostatic shunt device electrically connecting said leads, said device comprising an arm secured to one of said leads and in electrical contact with the other of said leads, said arm being responsive to temperature changes in said filament to break said electrical contact when said filament is thermally active.

3. An electric lamp for use in series lighting comprising, a. sealed enclosure, a pair 01' leads extending into said enclosure, a filament con meeting the ends 01 said leads, and a thermostatic shunt device electrically connecting said leads, said device comprising a bi-metallic arm secured to one oi said leads and in electrical contact with the other of said leads, said arm being responsive to temperature changes in said filament to break said electrical contact when said filament is thermally active and to maintain the said electrical contact when said filament is thermally inactive.

4. An electric lamp for use in series lighting comprising, a sealed enclosure, a pair of filament supporting leads extending into said enclosure, a filament connecting the ends of said leads, an arm mounted on each of said leads and within said enclosure, the free ends of said arms being in electrical contact with each other to establish a shunt path across said leads, at least one of said arms comprising a member responsive to temperature changes in said filament and operative to break said electrical contact when the filament is thermally active.

5. An electric lamp for use in series lighting comprising, a sealed enclosure, a pair of filament supporting leads extending into said enclosure, a filament connecting the ends of said leads, an arm mounted on each of said leads and within said enclosure, the free ends of said arms being in electrical contact with each other to establish a shunt path across said leads, at least one of said arms comprising a bi-metallic member responsive to temperature changes in said filament and operative to maintain said electrical contact when the filament is thermally inactive.

6. An electric lamp for use in series lighting comprising, a sealed enclosure, a pair of filament supporting leads extending into said enclosure, a filament connecting the ends of said leads, an arm mounted on each 01' said leads and within said enclosure, the free ends of said arms being in electrical contact with each other to establish a shunt path across said leads, each of said arms comprising a movable member responsive to temperature changes in said filament, said arms being operative to maintain said electrical contact when the filament is thermally inactive.

DORIS E. S'I'RATY. STEPHEN STRA'I'Y. 

